Adhesive composition and optical disc prepared therewith

ABSTRACT

The present invention provides an adhesive composition (a UV-curable resin composition) comprising a bisphenol type epoxy(meth)acrylate (A), a di(meth)acrylate compound (B) having a cyclic ether structure, and a photo-polymerization initiator (C), and a bonded optical disk which is adhered with a cured product of said adhesive composition. By adhering with said composition optical disk substrates having a translucent reflection film or a total reflection film comprising silver, a silver alloy, or the like, and obtaining a bonded optical disk, high durability equivalent to those of conventional bonded optical disks in which a translucent reflection film of gold is used, and high adhesion strength between a reflection film and an adhesive cured product, and a polycarbonate substrate and an adhesive cured product, can be obtained.

TECHNICAL FIELD

The present invention relates to an adhesive composition comprising aUV-curable adhesive composition suitable for bonding an optical disksubstrate, and especially it is useful for adhering two optical disksubstrates which are used for DVDs. The present invention relates alsoto an optical disk bonded with said adhesive composition.

BACKGROUND ART

DVDs in practical use at present can be roughly classified into DVD-ROMson which information such as movies has been recorded when producing thedisk, and blank DVDs on which no information is recorded upon productionallowing consumers themselves to record information on a pigmentrecording layer or an inorganic recording layer. As to DVD-ROMs,information is recorded on the substrates thereof, and they have typesas follows. They include DVD-5 with a structure of single-sided read andsingle recording layer having a recording capacity of about 5 GB, DVD-9of a single-sided read and dual recording layer having a recordingcapacity of about 9 GB, DVD-10 of a double-sided read and dual recordinglayer having a recording capacity of about 10 GB, and DVD-18 of adouble-sided read and quadruple recording layer having a recordingcapacity of about 18 GB. At present, DVD-9s are most commonly usedbecause of their recording capacity for recording a movie of about twoand a half hours. DVD-9s use a total reflection film and a translucentreflection film since it is a type of a single-sided read and dualrecording layer, and those using an aluminum alloy as a total reflectionfilm and gold as a translucent reflection film are most common. Unlike atotal reflection film, a translucent reflection film must transmitlaser, and so the film needs to be thin. Thus, gold, which can be easilyformed into a thin film and is relatively stable, has beenconventionally used.

Gold, however, is very expensive and therefore the material for atranslucent reflection film has been shifted from gold to silicon or asilicon compound, and further to silver or a silver alloy. In addition,use of blue lasers is now being developed for further increase ofrecording capacity. Optical disks of using conventional red lasers donot have any problem of laser transmittance even if a material for thetranslucent reflection film is gold, silicon, a silicon compound, silveror a silver alloy, and on the contrary for blue lasers, theirwavelengths reside in the vicinity of about 400 nm, and therefore amaterial for a translucent reflection film, which has good transmittanceof light having said wavelengths is limited to silver or a silver alloy.However, these have a disadvantage that they are more susceptible tooxidation and unstable than gold. When an optical disk wherein a thinfilm of silver or a silver alloy is used for a translucent reflectionfilm is allowed to adhere with a conventional resin composition for abonded optical disk, durability equivalent to those of bonded opticaldisks in which conventional gold is used as a material for thetranslucent reflection film, cannot be obtained. Therefore, an adhesivecomposition having satisfactory durability is requested to provide.

On the other hand, in the field of blank DVDs, there are various formatsincluding DVD−R, DVD+R,. DVD−RW, DVD+RW, and DVD-RAM. Presently dominantDVD−R, DVD-RAM, DVD+R and DVD+RW are of single-sided, single layerstructure, and those bonded with a polycarbonate substrate and asubstrate provided with a recording layer and a reflection film layer,are used. As a material for a reflection film layer, silver or a silveralloy, which has high reflectance, is used in a thickness to some extent(for example, 10 to 200 nm). Among new formats, there is a type havingtwo layers of a translucent reflection film layer and a total reflectionfilm layer, wherein silver or a silver alloy having high reflectance isused as a material for a reflection film layer. However, because silveror a silver alloy is subject to oxidation, a protective coat must beformed. Whereas formation of the protective coat can achieve highdurability, it has involved problems such as decrease of productionefficiency of optical disks, increase of production cost and decrease ofproduction yield. Development of an adhesive resin composition, whichcan afford equivalent durability without forming a protective coat, hasbeen desired.

Patent literature 1 describes a UV-curable adhesive composition suitablefor an optical disk, having as a main component a (meth)acrylate havingan alicyclic structure, and it is shown that durability in chemicalchange is improved such as oxidizing in a bonded optical disk using atranslucent reflection film layer such as of silver or a silver alloy.However, in a UV-curable adhesive composition suitable for an opticaldisk, having as a main component a (meth)acrylate having an alicyclicstructure, there has been a problem that adhesion between saidtranslucent reflection film and/or total reflection film and an adhesivecured product is weak.

Patent literature 1: JP-A-2001-167478

DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

The present invention aims at providing a resin composition for anadhesive, which affords, in a bonded optical disk having a totalreflection film or a translucent reflection film comprising silver, asilver alloy, or the like, high durability equivalent to those ofconventional optical disks in which gold is used for a translucentreflection film, and further has excellent adhesion between both of areflection film and a polycarbonate substrate, and an adhesive layer (anadhesive cured product).

MEANS FOR SOLVING THE PROBLEMS

The present inventors have conducted intensive studies to solve theabove-mentioned problems and as a result, have found an adhesivecomposition having excellent durability and adhesion even in a bondedoptical disk having a total reflection film or a translucent reflectionfilm comprising silver, a silver alloy, or the like, and thus haveaccomplished the present invention.

Accordingly, the present invention relates to:

-   (1) An adhesive composition comprising a bisphenol type    epoxy(meth)acrylate (A), a di(meth)acrylate compound (B) having a    cyclic ether structure, and a photo-polymerization initiator (C);-   (2) The adhesive composition according to the above-described (1),    which further comprises a (meth)acrylate phosphate compound (D);-   (3) The adhesive composition according to the above-described (1),    which further comprises a urethane(meth)acrylate (E);-   (4) The adhesive composition according to the above-described (1),    which comprises a bisphenol type epoxy(meth)acrylate (A), a    di(meth)acrylate compound (B) having a cyclic ether structure, a    photo-polymerization initiator (C), a (meth)acrylate phosphate    compound (D), and a urethane(meth)acrylate (E);-   (5) The adhesive composition according to the above-described (1),    which comprises, in terms of % by weight based on the total of the    adhesive composition, 1 to 70% of a bisphenol type    epoxy(meth)acrylate (A), 5 to 75% of a di(meth)acrylate compound (B)    having a cyclic ether structure, 0.05 to 20% of a    photo-polymerization initiator (C), and a residue of another    component;-   (6) The adhesive composition according to the above-described (1),    wherein the di(meth)acrylate compound (B) having a cyclic ether    structure is trimethylolpropane di(meth)acrylate modified with a    tertiary aldehyde having a carbon number of 4 to 10 which may have    hydroxy-substitution;-   (7) The adhesive composition according to the above-described (6),    wherein the di(meth)acrylate compound (B) having a cyclic ether    structure is a hydroxypivalic aldehyde modified trimethylolpropane    di(meth)acrylate;-   (8) A bonded optical disk, wherein two optical disk substrates are    adhered with a cured product of an adhesive composition according to    any one of the above-described (1) to (7); and-   (9) The bonded optical disk according to the above-described (8),    wherein at least one of the optical disk substrates is an optical    disk substrate having a total reflection film or a translucent    reflection film comprising silver or a silver alloy.

EFFECT OF THE INVENTION

By adhering optical disk substrates using a composition (a UV-curableresin composition) according to the present invention, in a bondedoptical disk using a translucent reflection film or a total reflectionfilm of silver or a silver alloy, high durability equivalent to those ofconventional bonded optical disks in which gold is used for atranslucent reflection film, can be obtained and further high adhesivestrength between a translucent reflection film or a total reflectionfilm and an adhesive cured product can be obtained. Moreover, amongblank DVDs such as DVD−R, DVD+R, DVD−RW, DVD+RW, DVD-RAM, and the like,in blank DVDs wherein silver or a silver alloy is used as a reflectionfilm, high durability equivalent to that on use of a protective coat canbe obtained, and further high adhesion strength between a metallicreflection film and an adhesive cured product, and a polycarbonatesubstrate and an adhesive cured product, can be obtained. Due to highadhesion strength, even by repeating use of DVDs, a bonded optical diskcannot be peeled.

BEST MODE OF EMBODIMENT TO CONDUCT THE INVENTION

An adhesive composition according to the present invention is suitablefor bonding an optical disk, and is a UV-curable resin composition whichcan be cured usually by light, especially by UV. Therefore, hereinafteran adhesive composition according to the present invention is sometimesdescribed as a UV-curable resin composition according to the presentinvention. Said composition is characterized by containing at leastthree of a bisphenol type epoxy(meth)acrylate (A), a di(meth)acrylatecompound (B) having a cyclic ether structure, and a photo-polymerizationinitiator (C). In this connection, in the present invention, “a(meth)acrylate”, “a (meth)acrylic acid”, and the like used in abisphenol type epoxy(meth)acrylate, (meth)acrylic acid, or the like,each means either one or both of a methacrylate and an acrylate, or of amethacrylic acid and an acrylic acid.

In the present invention, a bisphenol type epoxy(meth)acrylate (A) has afunction to improve a curing rate or to improve hardness of a curedproduct.

As a bisphenol type epoxy(meth)acrylate (A) contained in the compositionaccording to the present invention, an epoxy(meth)acrylate obtained by areaction of a bisphenol type epoxy resin, or the like, and a(meth)acrylic acid, for instance, by a reaction described below, isexemplified. As said bisphenol type epoxy resin, any one of bisphenoltype epoxy resins can be used, and a preferred one thereof includes abisphenol A type epoxy resin (for example, Epikoat 802, 1001, 1004(Trade name), and the like manufactured by Japan epoxy resins, Co.,Ltd.), or a bisphenol F type epoxy resin (for example, Epikoat 4001P,4002P, 4003P (Trade name), and the like manufactured by Japan epoxyresins, Co., Ltd.), and the like. A bisphenol A type epoxy resin is morepreferable. In this connection, a bisphenol type epoxy resin in (A)component does not include a modified product or a hydrogenated product,or the like thereof, and said modified product or hydrogenated product,or the like is contained in (B-1) component described below.

A preferable bisphenol type epoxy(meth)acrylate (A) can be obtained asfollows.

A bisphenol type epoxy resin, or the like and a (meth)acrylic acid arereacted in a ratio of 0.9 to 1.5 moles, more preferably 0.95 to 1.1moles, of (meth)acrylic acid based on 1 equivalent of epoxy group of thebisphenol type epoxy resin (a glycidyl ether type epoxy compound). Areaction temperature is preferably 80 to 120° C., and a reaction time isabout 10 to 35 hours. To facilitate the reaction, a catalyst such astriphenylphosphine, triethanolamine, tetraethylammonium chloride, or thelike is preferably used. In addition, to prevent a polymerization duringthe reaction, a polymerization inhibitor (e.g. paramethoxyphenol,methylhydroquinone, or the like) may be used.

The bisphenol type epoxy(meth)acrylate (A) may be used in an optionalratio of alone or a mixture of two sorts or more. A content of thebisphenol type epoxy(meth)acrylate (A) is usually 1 to 70% by weight,and preferably 5 to 40% by weight, more preferably 10 to 40% by weightbased on the total weight of the composition according to the presentinvention. A molecular weight of the bisphenol type epoxy(meth)acrylate(A) is preferably 500 to 10000.

A di(meth)acrylate compound (B) having a cyclic ether structurecontained in the composition according to the present invention is, forexample, a di(meth)acrylate having an alicyclic partial structurecontaining 1 to a plural number, preferably 1 to 4, more preferably 1 to2, of an oxygen atom, and is a di(meth)acrylate containing acyclic etherstructure of, preferably a 3 to 8 members ring, more preferably a 5 to 6members ring. Said di(meth)acrylate, due to effect of a position of acyclic ether has a function of enhancing adhesion between a metallicreflection film of such as silver, a silver alloy, aluminum, or the likeand an adhesive cured product, and a polycarbonate substrate and anadhesive cured product, can be obtained.

The di(meth)acrylate compound (B) having a cyclic ether structureincludes a hydroxy-substituted (C4 to C10) tertiary aldehyde modifiedtrimethylolpropane di(meth)acrylate or a modified product thereof,specifically a hydroxypivalic aldehyde modified trimethylolpropanedi(meth)acrylate (for example, KAYARAD R-604 manufactured by NIPPONKAYAKU Co., Ltd.) or a modified product thereof (for example, acaprolactone modified hydroxypivalic aldehyde modifiedtrimethylolpropane di(meth)acrylate, or the like), spiro-glycoldi(meth)acrylate, or the like. Preferably, it is a hydroxypivalicaldehyde modified trimethylolpropane di(meth)acrylate.

The (B) component can be used in an optional proportion of alone or amixture of at least two sorts thereof. A content of (B) component isusually 5 to 75% by weight (hereinafter % represents % by weight unlessnoted otherwise), preferably 10 to 60% or 70%, more preferably 35 to65%, based on the total weight of the composition according to thepresent invention.

In the UV-curable resin composition according to the present invention,a (meth)acrylate monomer (B-1) excluding the above-described (B)component, (D) component and (E) component described below (abbreviatedas “other acrylate” depending on cases), can be added. (B-1) componentincludes, for example, a mono-functional or multi-functional monomersuch as an ester of an alcohol having a carbon number of 1 to 15, whichmay have a substituent such as a hydroxyl group or an alkoxyl group,with a (meth)acrylic acid, and the like. Specifically, themono-functional monomer includes, for example,tricyclodecane(meth)acrylate, dicyclopentadiene oxyethyl(meth)acrylate,dicyclopentanyl(meth)acrylate, isobornyl(meth)acrylate,adamantyl(meth)acrylate, phenoxyethyl(meth)acrylate, phenoxypolyethyleneglycol(meth)acrylate, benzyl(meth)acrylate,tetrahydrofurfuryl(meth)acrylate, morpholine(meth)acrylate, 2-hydroxypropyl(meth)acrylate, lauryl(meth)acrylate, isodecyl(meth)acrylate,stearyl(meth)acrylate, isooctyl(meth)acrylate, tridecyl(meth)acrylate,ethoxydiethyrene glycol(meth)acrylate, and the like.

Further as (B-1) component, a multi-functional (meth)acrylate monomerwhich has at least two (meth) acrylate groups in the molecule thereofincludes, for example, cyclohexane-1,4-dimethanol di(meth)acrylate,cyclohexane-1,3-dimethanol di(meth)acrylate, tricyclodecane-dimethyloldi(meth)acrylate (for example, KAYARAD R-684 manufactured by NIPPONKAYAKU Co., Ltd., tricyclodecane-dimethylol diacrylate, and the like), ahydrogenated bisphenol A polyethoxy-di(meth)acrylate, a hydrogenatedbisphenol A polypropoxy-di(meth)acrylate, a hydrogenated bisphenol Fpolyethoxy-di(meth)acrylate, a polyethoxy-di(meth)acrylate ofcyclohexane-1,4-dimethanol, a di(meth)acrylate of an adduct withε-caprolactone of hydrogenated bisphenol A, a di(meth)acrylate of anadduct with ε-caprolactone of cyclohexane-1,4-dimethanol, adi(meth)acrylate of hydrogenated bisphenol A diglycidyl ether, adi(meth)acrylate of hydrogenated bisphenol F diglycidyl ether, adi(meth)acrylate of hydrogenated bisphenol A diglycidyl ether, adi(meth)acrylate of hydrogenated bisphenol F diglycidyl ether, neopentylglycol di(meth)acrylate, a polyethylene glycol di(meth)acrylate,dicyclopentanyl di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, apolypropylene glycol di(meth)acrylate, an ethylene oxide modifiedbisphenol A di(meth)acrylate, an ethylene oxide modified trimethylolpropane tri(meth)acrylate, an ethylene oxide modified pentaerythritoltetra(meth)acrylate, tris[(meth)acryloxyethyl]isocyanurate, an ethyleneoxide modified dipentaerythritol hexa(meth)acrylate, and the like.

The (meth)acrylate monomer (B-1) can be used in an optional proportionof alone or a mixture of at least two sorts thereof. A content of said(meth)acrylate monomer (B-1) is usually 0 to 85%, preferably 0 to 60%,more preferably 0 to 40%, based on the total weight of the compositionaccording to the present invention. Depending on cases, 10 to 60% ispreferred.

As a photo-polymerization initiator (C) contained in the compositionaccording to the present invention, 1-hydroxycyclohexyl phenyl ketone,2,2-dimethoxy-2-phenylacetophenodroxy-2-methyl-1-phenylpropane-1-one,1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one or2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propane is preferable,and it can be used in an optional proportion of alone or a mixture of atleast two sorts thereof. A content of the photo-polymerization initiator(C) is usually 0.5 to 20%, preferably 1 to 10%, based on the totalweight of the composition according to the present invention.

Further, in the present invention, other photopolymerization initiatorsmay be used together if necessary. As a preferable one, the followingcan be exemplified. For example, it includes2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one,2-chlorothioxanthone, 2,4-dimethylthioxanethone,2,4-diisopropylthioxanthone, isopropylthioxanthone,2,4,6-trimethylbenzoyldiphosphine oxide andbis(2,6-dimethoxy-benzoyl)-2,4,4-trimethylpentylphosphine oxide, and thelike. The photopolymerization initiator may be used in an optionalproportion of alone or a mixture of at least two sorts thereof. Thecontent thereof is usually 0 to 5%, 0.005 to 5% depending on cases, andpreferably 0 to 5%, 0.01 to 3% depending on cases based on the totalweight of the composition according to the present invention.

In addition, amines or the like which can be a photopolymerizationaccelerator may also be used together with the above-describedphotopolymerization initiator. The amines or the like which can be usedinclude 2-dimethylaminoethyl benzoate, dimethylaminoacetophenone, ethylp-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, and the like.When the photopolymerization accelerator such as said amines is used,the content thereof is usually 0 to 5%, 0.005 to 5% depending on cases,and preferably 0 to 3%, 0.01 to 3% depending on cases based on the totalweight of the composition according to the present invention.

To the UV-curable resin composition according to the present invention,a (meth)acrylate phosphate compound (D) may be added if necessary. The(meth)acrylate phosphate compound (D) has a function to improve anadhesive property between aluminum, silver, or a silver alloy and anadhesive cured product, but attention is necessary to an amount to beused, since it has a fear of corroding a metallic film.

The (meth)acrylate phosphate compound (D) which can be contained in thecomposition according to the present invention, may be a monoester,diester, trimester or the like, and is not limitative so long as it is a(meth)acrylate having a phosphoric ester bone. For instance, apreferable one thereof includes C1 to C3 alkylene oxide modified C6 toC10 aryloxy or C1 to C10 alkoxy mono-, di-, or tri-(meth)acrylatephosphate, and for example, it includes ethylene oxide modifiedphenoxide(meth)acrylate phosphate, ethylene oxide modifiedbutoxide(meth)acrylate phosphate, ethylene oxide modified octyloxide(meth)acrylate phosphate, and C1 to C3 alkylene oxide modifiedmono-, di-, or tri-(meth)acrylate phosphate including ethylene oxidemodified di(meth)acrylate phosphate and ethylene oxide modifiedtri(meth)acrylate phosphate, and the like. Among these, a C1 to C3alkylene oxide modified mono-, di-, or tri-(meth)acrylate phosphate ispreferable. C1 to C3 alkylene oxide modified mono-, di-, ortri-(meth)acrylate phosphate is more preferable. The (meth)acrylatephosphate (D) may be used in an optional proportion of alone or amixture of at least two sorts thereof. The content of(meth)acrylatephosphate compound (D) is usually 0 to 5%, 0.005 to 5%depending on cases, and preferably 0 to 3%, 0.05 to 3% depending oncases, based on the total weight of the composition according to thepresent invention.

To the composition according to the present invention, aurethane(meth)acrylate (E) may be added if necessary. Theurethane(meth)acrylate (E) further improves adhesion and improvesflexibility of adhesive cured film as well. Therefore, by making (E)component contained, warp of bonded optical disks obtained can be madesmall. The urethane(meth)acrylate (E) in the present invention can beobtained by reacting a polyhydric alcohol, an organic polyisocyanate anda hydroxy(meth)acrylate compound.

The polyhydric alcohol includes, for example, a C1 to C10 alkyleneglycol such as neopentyl glycol, 3-methyl-1,5-pentanediol, ethyleneglycol, propylene glycol, 1,4-butanediol, and 1,6-hexanediol, analiphatic polyol, preferably a C1 to C15, more preferably a C2 to C12aliphatic polyol, such as trimethylolpropane, pentaerythritol,tricyclodecane dimethylol and bis-[hydroxymethyl]-cyclohexane; apolyester polyol obtained by a reaction of the polyhydric alcohol and apolybasic acid, preferably a C3 to C12 polybasic acid (e.g. a succinicacid, a phthalic acid, a hexahydrophthalic anhydride, a terephthalicacid, an adipic acid, an azelaic acid and a tetrahydrophthalicanhydride); a caprolactone alcohol obtained by a reaction of theabove-described aliphatic polyol and ε-caprolactone; a polycarbonatepolyol obtained by a reaction of the above-described aliphatic polyoland a carbonate (e.g. a polycarbonate diol obtained by a reaction of1,6-hexanediol and a diphenylcarbonate); and a polyether polyol (e.g.poly alkylene glycol such as a polyethylene glycol, a polypropyleneglycol, a polytetramethylene glycol and the like; preferably poly C1 toC6 alkylene glycol, an ethylene oxide modified bisphenol A and thelike); and the like.

The organic polyisocyanate includes, for example, a compound wherein atleast 2 isocyanate groups, preferably 2 to 4 isocyanate groups, arelinked with a hydrocarbon residue having a carbon number of 1 to 20,preferably C6 to C15, and specifically it includes isophoronediisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, xylenediisocyanate, diphenyl methane-4,4′-diisocyanate, dicyclopentanyldiisocyanate, and the like.

The hydroxy(meth)acrylate compound include, for example, a hydroxysubstituted C1 to C15 hydrocarbon(meth)acrylate, preferably a hydroxysubstituted C2 to C10 hydrocarbon(meth)acrylate, and specifically itincludes hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate,hydroxybutyl(meth)acrylate, dimethylolcyclohexyl mono(meth)acrylate,hydroxycaprolactone(meth)acrylate, and the like.

The urethane(meth)acrylate (E) can be obtained by a reaction as follows.That is, an organic polyisocyanate is mixed with a polyhydric alcohol sothat an amount of an isocyanate group is 1.1 to 2.0 equivalents per 1equivalent of a hydroxyl group, and the reaction is conducted at areaction temperature of preferably 70 to 90° C. to produce a urethaneoligomer. Then a hydroxy(meth)acrylate compound is added so that anamount of a hydroxyl group is preferably 1 to 1.5 equivalents per 1equivalent of an isocyanate group of the urethane oligomer obtained, andthe reaction is conducted preferably at a reaction temperature of 70 to90° C. to obtain an aimed urethane(meth)acrylate (E).

The urethane(meth)acrylate (E) may be used in an optional proportion ofalone or a mixture of at least two sorts thereof. The content ofurethane(meth)acrylate (E) is 0 to 50%, 1 to 50% depending on cases, andpreferably 0 to 40%, 5 to 40% depending on cases, based on the totalweight of the composition according to the present invention. Amolecular weight of the urethane(meth)acrylate (E) is preferably 400 to10,000.

In this connection, in the present invention, a molecular weight means aweight average molecular weight, and a measuring method depends on alight scattering method.

The composition according to the present invention may contain anantioxidant (F), and the antioxidant includes, for example, a hinderedphenol compound, an amine compound, a sulfur compound and/or aphosphorus compound, and the like.

Specific examples of the hindered phenol compound as an antioxidant (F)include 2,6-di-tert-butyl-4-methylphenol,2,2′-methylene-bis(4-methyl-6-tert-butylphenol),2,2′-methylene-bis(4-ethyl-6-tert-butylphenol),4,4′-thio-bis(3-methyl-6-tert-butylphenol),4,4′-butylidene-bis(3-methyl-6-tert-butylphenol), triethylene glycolbis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate], 1,6-hexanediolbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate,3,5-di-tert-butyl-4-hydroxybenzyl phosphonate-diethyl ester,1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,isooctyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and the like.

Specific examples of the amine compound as an antioxidant (F) includeoctylated diphenylamine(for example, 4,4′-dioctyl-diphenylamine, and thelike), 4,4′-dicumyl-diphenylamine,6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline,2,2,4-trimethyl-1,2-dihydroquinoline polymer, and the like.

Specific examples of the sulfur compound as an antioxidant (F) include2-mercaptobenzimidazole, 2,4-bis[(octylthiomethyl)-o-cresol,2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine, and ADKSTAB AO-412S (manufactured by AsahiDenka Co., Ltd.) and the like.

Specific examples of the phosphorus compound as an antioxidant (F)include tris(nonylated phenyl)phosphite, ADKSTAB PER-4C (manufactured byAsahi Denka Co., Ltd.), ADKSTAB 260 (manufactured by Asahi Denka Co.,Ltd.), ADKSTAB 522A (manufactured by Asahi Denka Co., Ltd.), and thelike.

Among these antioxidant (F), as a particularly preferable one, ahindered phenol compound can be enumerated. One or at least two sorts ofthese antioxidants can be used. The content of the antioxidant (F) isusually 0 to 10%, 0.005 to 10% depending on cases, and preferablyusually 0 to 5%, 0.01 to 5% depending on cases, based on the totalweight of the composition according to the present invention.

Further, as other additives, as a polymer to the composition of thepresent invention, a polyester-, polycarbonate-, polyacrylic-,polyurethane- or polyvinyl-based resin may be added.

Moreover, additives such as an organic solvent, a silane coupling agent,a polymerization inhibitor, a leveling agent, an antistatic agent, asurface lubricant, a fluorescent whitening agent, a light stabilizer(for example, a hindered amine compound, or the like), and a filler maybe added. These other additives are contained to an extent of usually 0to 10%, preferably 0 to 5%.

Preferable examples of the composition according to the presentinvention includes, based on the total weight of the adhesivecomposition, the composition which comprises, of 1 to 70%, preferably of5 to 40%, more preferably of 10 to 40%, of a bisphenol typeepoxy(meth)acrylate (A), preferably a bisphenol A type epoxy resin;

-   5 to 75%, preferably 10 to 70%, more preferably 35 to 65%, of a    di(meth)acrylate compound (B) having a cyclic ether structure,    preferably a di(meth)acrylate having an alicyclic partial structure    having 1 to 4, more preferably 1 to 2, of oxygen atoms, preferably a    di(meth)acrylate containing a cyclic ether structure having a ring    of 3 to 8 members, more preferably of 5 to 6 members, further    preferably a hydroxypivalic aldehyde modified trimethylolpropane    di(meth)acrylate; 0.05 to 20%, preferably 1 to 10%, of a    photo-polymerization initiator (C); and-   a residue of another component.

As the other additives as described above, a (meth)acrylate phosphatecompound (D), a urethane(meth)acrylate (E), a (meth)acrylate monomer(B-1) (abbreviated as “other acrylate” depending on cases) excluding theabove described (B) component, (D) component, and (E) component, anantioxidant (F), and other additives may be exemplified. Among these, acomposition containing a (meth)acrylate phosphate compound (D) and aurethane(meth)acrylate (E) is preferred. Additionally, a compositioncontaining (B-1) component is one of preferable embodiments. Examples ofthe content of these based on the total weight of the compositionaccording to the present invention are as described below:

-   A (meth)acrylate phosphate compound (D), preferably a Cl to C3    alkylene oxide modified mono-, di-, or tri(meth)acrylate, more    preferably a C1 to C3 alkylene oxide modified di(meth)acrylate    phosphate: usually 0 to 5%, 0.005 to 5% depending on cases, and    preferably 0 to 3%, 0.05 to 3% depending on cases;-   A urethane(meth)acrylate (E) : 0 to 50%, 1 to 50% depending on    cases, and preferably 0 to 40%, 5 to 40% depending on cases; and-   An other acrylate (B-1) component: 0 to 85% preferably 0 to 60%,    more preferably 0 to 40%.

The composition according to the present invention can be obtained bymixing and dissolving each component described above at room temperatureto 80° C., and impurities may be removed if necessary by operation suchas filtration. The viscosity at 25° C. of the composition according tothe present invention is preferably in the range of 100 to 5000 mPa·s(measured by a Brookfield type viscometer) when considering a coatingproperty.

The composition according to the present invention can suitably be usedas an adhesive for a bonded optical disk, especially as an adhesive usedon bonding optical disk substrates either one or both of which have atotal reflection film or a translucent reflection film of silver or asilver alloy. Specifically, the composition is applied on optical disksubstrates by any method such as a spin coating method, a 2P method, aroll coating method, and a screen printing method, and two optical disksubstrates are bonded so that a film thickness of an adhesive layerbecomes 1 to 100 μm after bonding, and then by irradiating with rayssuch as ultraviolet to near ultraviolet rays (a wave length in thevicinity of 250 to 400 nm) from one or both sides, the adhesive layer iscured to bond the substrates. The irradiation amount is preferably 50 to1000 mJ/cm², particularly preferably nearly 100 to 700 mJ/cm². Forirradiation with ultraviolet to near ultraviolet rays, the light sourceis not particularly limited so long as it is a lamp which emitsultraviolet to near ultraviolet rays. For example, a low pressure, highpressure or ultra-high pressure mercury lamp, a metal halide lamp, a(pulse) xenon lamp or an electrodeless lamp, or the like may beexemplified.

As an optical disk substrate, those already known, namely those whereingold is used, or silicon, a silicon compound, silver, a silver alloy, orthe like is used, as a translucent reflection film, can be used.Especially, the composition according to the present invention cansuitably be used for a bonded optical disk wherein silver or a silveralloy is used as a total reflection film or a translucent reflectionfilm.

In the present invention, a bonded optical disk which is adhered with acured product of the above-described composition according to thepresent invention, is contained. Particularly, a bonded optical diskwherein at least one of optical disk substrates has a total reflectionfilm or a translucent reflection film of silver or a silver alloy, andthe optical disk substrates are adhered with a cured product of theabove-described composition according to the present invention, iscontained therein. Said optical disk is used for DVDs, and the like suchas DVD−ROM (DVD-5,. DVD-10, DVD-9, DVD-14, and DVD-18), DVD−R, DVD+R,DVD−RW, DVD+RW, DVD-RAM, DVD−R single-sided and double layer manner,DVD+R single-sided and double layer manner, DVD−RW single-sided anddouble layer manner, DVD+R single-sided and double layer manner, and thelike.

EXAMPLES

Hereinafter the present invention is more specifically explained by wayof examples, but the present invention should not in the least belimited by these Examples. In this connection, “part” in Example andTable mean “part by weight” unless noted otherwise.

Example 1

In a reactor equipped with a stirrer and a thermometer, 30 parts ofbisphenol A diglycidylether diacrylate (EPA-37) (A), 60 parts of ahydroxypivalic aldehyde modified trimethylolpropane diacrylate (R-604)(B), 9 parts of 2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE 651)(C), 30 parts of dicyclopentadiene oxyethyl acrylate (FA-512A)(B-1), 0.1part of an ethylene oxide modified dimethacrylate phosphate (PM-2) (D),and 5 parts of a polyether-based urethane acrylate (UA-732) (E), weremixed and dissolved at 60° C. for one hour to prepare a compositionaccording to the present invention. At this time, a viscosity of thecomposition of the present invention was at 25° C. 500 mPa·s (measuredby a Brookfield type viscometer).

A bonded optical disk of a DVD-9 type was prepared by adhering twooptical disk substrates using this composition according to theprocedures 1 to 4 described below (in accordance with necessity, asubstrate wherein a pit for recorded information is formed was used). Inthe same way, a bonded optical disk of a DVD+R type was prepared byadhering two optical disk substrates using this composition according tothe procedures 5 to 8 described below.

1. A silver alloy translucent reflection film substrate (a DVDsubstrate) was prepared by sputtering (hereinafter described as“sputtering”) a silver alloy (TTP-55A manufactured by Target TechnologyCompany LLC) on a 0.6 mm thick polycarbonate (hereinafter described as“PC”) substrate so as to make an average film thickness of 10 nm.

Further an aluminum alloy total reflection film substrate (a DVDsubstrate) was prepared by sputtering an aluminum alloy (manufactured byUnaxis) on a 0.6 mm thick PC substrate so as to make an average filmthickness of 45 nm.

2. Along the circumference in the total reflection film DVD substrateobtained in the above-described, a circle was drawn with 2.5 g of theadhesive composition (a UV-curable resin composition).

3. The translucent reflection film DVD substrate obtained in theabove-described 1 was put on the aluminum alloy substrate (with thesputtering surface upward) so that the sputtering surface of said DVDsubstrate was downward, and spin-coating was conducted for 4 seconds ata rate of 2000 rpm to bond them so that a film thickness of the resincomposition between the silver alloy translucent reflection film and thealuminum alloy may become 45 to 65 μm. An apparatus manufactured byOrigin ELECTRIC CO., LTD. was used.

4. By using upper and lower two xenon flash lamps, irradiation of 8shots at 1800 V was conducted with the upper lamp and irradiation of 4shots at 1600 V was conducted with the lower lamp. Said disk substrateswere adhered by curing of the resin composition and obtained a bondedoptical disk of a DVD-9 type. In this connection, the DVD disk waspositioned with the silver alloy translucent reflection film on theupper side and the aluminum alloy total reflection film on the lowerside.

5. To prepare a bonded optical disk of a DVD+R type, an azo pigmentrecording layer was formed by a spin-coating method on a 0.6 mm thick PCsubstrate wherein a pit for DVD+R is formed, and after drying it at 80°C. for 15 min, a silver reflection film substrate was prepared bysputtering silver (manufactured by Unaxis) so as to make an average filmthickness of 100 nm.

6. Along the circumference in the silver reflection film substrate, acircle was drawn with 2.5 g of the adhesive composition (a UV-curableresin composition)

7. The 0.6 mm thick PC substrate was put on the silver reflection filmsubstrate obtained in the above-described 6 (with the sputtered surfaceupward), and spin-coating was conducted for 4 seconds at a rate of 3000rpm to bond them so that a film thickness of the resin compositionbetween the PC substrate and the silver reflection film may become 35 to55 μm. An apparatus manufactured by Origin ELECTRIC CO., LTD. was used.

8. By using a xenon flash lamp, irradiation of 8 shots at 1800 V wasconducted from the upper side. Said disk substrates were adhered bycuring of composition and obtained a bonded optical disk of a DVD+Rtype. In this connection, the DVD disk was positioned with the PCsubstrate on the upper side and the silver reflection film substrate onthe lower side.

9. On the DVD+R substrates prepared according to the above-described 5to 8, a signal of about 4.7 gigabytes was recorded at a writing speed of8 times rate by a drive (Type:PX-708A) manufactured by PLEXSTAR Inc.

Example 2

The composition according to the present invention in Table 1 wasprepared in the same way as Example 1 except that 30 parts of bisphenolA diglycidylether diacrylate (EPA-37) (A), 60 parts of a hydroxypivalicaldehyde modified trimethylolpropane diacrylate (R-604) (B), 9 parts of1-hydroxycyclohexyl phenyl ketone (IRGACURE 184) (C), 30 parts ofdicyclopentadiene oxyethyl acrylate (FA-512A) (B-1), 0.1 part of anethylene oxide modified dimethacrylate phosphate (PM-2) (D), and 5 partsof a polyether-based urethane acrylate (UA-732) (E) were used, andsubsequently a bonded optical disk was prepared in the same way asExample 1.

Example 3

The composition according to the present invention in Table 1 wasprepared in the same way as Example 1 except that 10 parts of bisphenolA diglycidylether diacrylate (EPA-37) (A), 50 parts of a hydroxypivalicaldehyde modified trimethylolpropane diacrylate (R-604) (B), 7 parts of2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE 651) (C), 0.1 part of anethylene oxide modified dimethacrylate phosphate (PM-2) (D), 10 parts oftris(acryloxyethyl)isocyanurate (M-315) (B-1), 10 parts of an EO(ethylene oxide) modified bisphenol A diacrylate (R-551), and 5 parts ofa polyether-based urethane acrylate (UA-732) (E) were used, andsubsequently a bonded optical disk was prepared in the same way asExample 1.

Example 4

The composition according to the present invention in Table 1 wasprepared in the same way as Example 1 except that 30 parts of bisphenolA diglycidylether diacrylate (EPA-37) (A), 60 parts of a hydroxypivalicaldehyde modified trimethylolpropane diacrylate (R-604) (B), 9 parts of2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butane-1-one (IRGACURE907) (C), 0.1 part of an ethylene oxide modified dimethacrylatephosphate (PM-2) (D), and 5 parts of a polyether-based urethane acrylate(UA-732) (E) were used, and subsequently a bonded optical disk wasprepared in the same way as Example 1.

Comparative Example 1

The composition for Comparative Example, which does not contain adi(meth)acrylate compound (B) having a cyclic ether structure andcontains a (meth)acrylate compound having an alicyclic structure(tricyclodecanedimethylol diacrylate: R-684) in Table 1, was prepared inalmost the same way as Example 1 except that 30 parts of bisphenol Adiglycidylether diacrylate (EPA-37) (A), 9 parts of 1-hydroxycyclohexylphenyl ketone (IRGACURE 184) (C), 30 parts of dicyclopentadiene oxyethylacrylate (FA-512A)(B-1), 0.1 part of an ethylene oxide modifieddimethacrylate phosphate (PM-2) (D), and 60 parts oftricyclodecanedimethylol diacrylate (R-684) were used, and subsequentlya bonded optical disk was prepared in the same way as Example 1. TABLE 1Example Comp. Ex. 1 2 3 4 1 EPA-37 30 30 10 30 30 R-604 60 60 50 60IRGACURE 651 9 7 IRGACURE 184 9 9 IRGACURE 907 9 FA-512A 30 30 30 PM-20.1 0.1 0.1 0.1 0.1 M-315 10 R-684 60 R-551 10 UA-732 5 5 5 5 Viscosity500 490 530 520 (mPa · s, 25° C.)

In this connection, each composition abbreviated in Table 1 is asfollows. And a number showing a composition in Table 1 represents partby weight. EPA-37: bisphenol A diglycidyl ether diacrylate manufacturedby NIPPON KAYAKU CO., LTD., R-604: a hydroxypivalic aldehyde modifiedtrimethylolpropane diacrylate manufactured by NIPPON KAYAKU CO., LTD,IRGACURE 651: 2,2-dimethoxy-1,2-diphenylethan-1-one manufactured by CibaSpecialty Chemicals, IRGACURE 184: 1-hydroxycyclohexyl phenyl ketonemanufactured by Ciba Specialty Chemicals, IRGACURE 907:2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butane-1-onemanufactured by Ciba Specialty Chemicals, FA-512A: dicyclopentadieneoxyethyl acrylate manufactured by Hitachi Chemical Co., Ltd., PM-2:anethylene oxide modified dimethacrylate phosphate manufactured by NIPPONKAYAKU CO., LTD., M-315: tris(acryloxyethyl)isocyanurate manufactured byTOAGOSEI Co., Ltd., R-684: tricyclodecanedimethylol diacrylatemanufactured by NIPPON KAYAKU CO., LTD. R-551: an EO (ethylene oxide)modified bisphenol A diacrylate manufactured by NIPPON KAYAKU CO., LTD.UA-732: a polyether-based urethane acrylate manufactured by NIPPONKAYAKU CO., LTD.

Testing Examples

Bonded optical disks obtained in Examples or Comparative Examples wereevaluated according to the following method.

1. Appearance of a Reflection Film Before and After Durability Test(Common to DVD-9 and DVD+R)

A bonded optical disk obtained was left in an environment of 80° C. and85% RH (relative humidity) for 500 hours and 700 hours. A state of areflection film was visually observed. The observation results wereassessed as follows and shown in Table 2:

-   G: Compared to those immediately after adhesion, no change was    observed in the total reflection film or the translucent reflection    film in the evaluation after 700 hours;-   M: Compared to those immediately after adhesion, no change was    observed in the total reflection film or the translucent reflection    film in the evaluation after 500 hours, but considerable    discoloration or pinholes were found in the total reflection film    and the translucent reflection film in the evaluation after 700    hours; and-   P: Compared to those immediately after adhesion, considerable    discoloration or pinholes were found in the total reflection film    and the translucent reflection film in the evaluation after 500    hours.    2. Electric Signal of an Optical Disk Before and After Durability    Test    DVD-9:

A bonded optical disk obtained was left in an environment of 80° C. and85% RH for 700 hours. The electric signal of the bonded optical diskafter the durability test was evaluated using a DVD data signalmeasuring device DVD-2000 manufactured by AECO, Ltd.

“System jitter” and “PI error” are one of electric signals from anoptical disk, and the larger the value, the more deteriorated the dataof the bonded optical disk is shown:

-   G: system jitter of not more than 8.0 and PI error of not more than    250;-   M: system jitter of 8.1 to 9.0 and PI error of 251 to 350; and-   P: system jitter of not less than 9.1 and PI error of not less than    351.    DVD+R:

A bonded optical disk obtained was left in an environment of 80° C. and85% RH for 480 hours. The electric signal of the bonded optical diskafter the durability test was evaluated using a DVD data signalmeasuring device DVD-CATS SA-300 manufactured by AudioDeb AB.

“Tilt jitter” and “PISum8” are one of electric signals from an opticaldisk, and the larger the value, the more deteriorated the data of thebonded optical disk is shown:

-   G: tilt jitter of not more than 8.0 and PISum8 of not more than 250;-   M: tilt jitter of 8.1 to 9.0 and PISum8 of 251 to 350; and-   P: tilt jitter of not less than 9.1 and PISum8 of not less than 351.    3. Evaluation of Adhesion with a Reflection Film DVD-9:

Adhesion strength with an adhesive between a reflection film and anoptical disk substrate of a bonded optical disk obtained was evaluated.The evaluation was conducted as follows. At a bonded interfacial part ofthe bonded optical disk obtained, a small notch of about 5 mm depth wasmade with a cutter, the bonded optical disk was peeled with a fingerfrom the notch, and a state of the reflection film after the peeling wasobserved:

-   G: adhesion is excellent, and on peeling, not less than half of a    translucent reflection film or a total reflection film was peeled    from a polycarbonate substrate;-   M: adhesion is insufficient, and on peeling, only a portion of a    translucent reflection film or a total reflection film was peeled    from a polycarbonate substrate; and-   P: adhesion is weak, and on peeling, almost all of a reflection film    was not peeled from a polycarbonate substrate.    DVD+R:

Adhesion strength with an adhesive between a reflection film and anoptical disk substrate of a bonded optical disk obtained was evaluated.The evaluation was conducted as follows. At a bonded interfacial part ofthe bonded optical disk obtained, a small notch of about 5 mm depth wasmade with a cutter, the bonded optical disk was peeled with a fingerfrom the notch, and a state of the reflection film after the peeling wasobserved:

-   G: adhesion is excellent, and on peeling, not less than half of a    total reflection film was peeled from an interface with a pigment    layer;-   M: adhesion is insufficient, and on peeling, only a portion of a    total reflection film was peeled from an interface with a pigment    layer; and-   P: adhesion is weak, and almost all of a reflection film was not    peeled from an interface with a pigment layer.

The evaluation result with DVD-9 is described in Table 2. TABLE 2Example Comp. Ex. 1 2 3 4 1 1. Appearance of a G G G G G reflection filmbefore and after durability test 2. Electric signal of an G G G G Goptical disk before and after durability test 3. Evaluation of adhesionG G G G P with a reflection film

The evaluation result with DVD+R is described in Table. 3. TABLE 3Example Comp. Ex. 1 2 3 4 1 1. Appearance of a G G G G G reflection filmbefore and after durability test 2. Electric signal of an G G G G Goptical disk before and after durability test 3. Evaluation of adhesionG G G G P with a reflection film

The results of Table 2 and Table 3 exhibit that an optical disk adheredby using the composition according to the present invention containing adi(meth)acrylate compound having a cyclic ether structure, hasparticularly excellent adhesion between a reflection film and a UV curedproduct.

INDUSTRIAL APPLICABILITY

By adhering optical disk substrates using a composition (a UV-curableresin composition) according to the present invention, in a bondedoptical disk using a translucent reflection film or a total reflectionfilm of silver or a silver alloy, high durability equivalent to those ofconventional bonded optical disks in which gold is used for atranslucent reflection film, can be obtained and further high adhesionstrength between a translucent reflection film or a total reflectionfilm and an adhesive cured product can be obtained. Moreover, amongblank DVDs such as DVD−R, DVD+R, DVD−RW, DVD+RW, DVD-RAM, and the like,in blank DVDs wherein silver or a silver alloy is used as a reflectionfilm, high durability equivalent to that on use of a protective coat canbe obtained, and further high adhesion strength between a metallicreflection film and an adhesive cured product, and a polycarbonatesubstrate and an adhesive cured product, can be obtained. Due to highadhesion strength, even by repeating use of DVDs, a bonded optical diskcannot be peeled.

1. An adhesive composition comprising a bisphenol typeepoxy(meth)acrylate (A), a di(meth)acrylate compound (B) having a cyclicether structure, and a photo-polymerization initiator (C).
 2. Theadhesive composition according to claim 1, which further comprises a(meth)acrylate phosphate compound (D).
 3. The adhesive compositionaccording to claim 1, which further comprises a urethane(meth)acrylate(E)
 4. The adhesive composition according to claim 1, which comprises abisphenol type epoxy(meth)acrylate (A), a di(meth)acrylate compound (B)having a cyclic ether structure, a photo-polymerization initiator (C), a(meth)acrylate phosphate compound (D), and a urethane(meth)acrylate (E).5. The adhesive composition according to claim 1, which comprises, interms of % by weight based on the total of the adhesive composition, 1to 70% of a bisphenol type epoxy(meth)acrylate (A), 5 to 75% of adi(meth)acrylate compound (B) having a cyclic ether structure, 0.05 to20% of a photo-polymerization initiator (C), and a residue of anothercomponent.
 6. The adhesive composition according to claim 1, wherein thedi(meth)acrylate compound (B) having a cyclic ether structure is ahydroxy-substituted (C4 to C10) tertiary aldehyde modifiedtrimethylolpropane di(meth)acrylate or a modified product thereof. 7.The adhesive composition according to claim 6, wherein thedi(meth)acrylate compound (B) having a cyclic ether structure is ahydroxypivalic aldehyde modified trimethylolpropane di(meth)acrylate. 8.A bonded optical disk, wherein two optical disk substrates are adheredwith a cured product of an adhesive composition according to anyone ofclaims 1 to
 7. 9. The bonded optical disk according to claim 8, whereinat least one of the optical disk substrates is an optical disk substratehaving a total reflection film or a translucent reflection filmcomprising silver or a silver alloy.